1. Field of Use
This invention relates generally to a connecting rod in the drive connection between a crank shaft and a piston in a gas compressor or the like.
In particular, it relates to the construction of the crank pin on the crank shaft and to the construction of a two-piece bearing assembly employed in a crank pin receiving hole in the connecting rod.
2. Description of the Prior Art
Some machines, such as reciprocating type internal combustion (IC) engines and gas compressors or the like, employ a rotatable crank shaft, a reciprocably movable piston and a connecting rod which transmits motion therebetween. Typically, the connecting rod has a cylindrical crank pin hole at one end for receiving a cylindrical crank pin of the crank shaft and a wrist pin hole at the opposite end for receiving the wrist pin of the piston. When the system is in operation, the crank shaft rotates, the crank pin travels in a circular path and also exhibits oscillatory motion relative to the crank pin hole and the connecting rod and piston exhibit generally reciprocating motion. Usually, a one or two-piece friction-reducing bearing assembly is employed in the crank pin hole of the connecting rod around the crank pin and lubricating oil is supplied thereto under pressure from a pump through passages in the crank pin. In an IC engine, reciprocating movement of the piston and connecting rod on a power stroke effects rotation of the crank shaft. In a two-cycle IC engine there is one power/intake stroke and one compression/exhaust stroke of the connecting rod for each revolution of the crank shaft. In a four-cycle IC engine there is one power/intake stroke or one compression/exhaust stroke of the connecting rod for each crank shaft revolution. Conversely, in a compressor, rotational movement of the crank shaft (imparted by a motor) effects reciprocating movement of the connecting rod and piston. In a typical two-cycle compressor there is one compression stroke and one intake stroke of the connecting rod for each revolution of the crank shaft. In both an IC engine and a compressor, maximum force or pressure is applied to the side of the crank pin closest to the piston during the power stroke and during the compression stroke and this side of the crank pin tends to exhibit the most wear. The pressure is applied either by an adjacent side of the crank pin hole or by the bearing therearound. The compressive and wear forces acting on the crank pin and its bearing in a large compressor are often substantially higher and of greater frequency than those in a comparably sized four-cycle IC engine. Furthermore, since the lubricating oil temperature in an IC engine is much higher than that in a compressor, oil in the compressor is more viscous, (assuming oil of the same type and weight) and lubrication can pose problems, especially between two metal surfaces which are being forced together at great pressure on the order of 1000 psi.
Some prior art friction-reducing bearing assemblies for the connecting rod in the compressor comprise two semi-circular bearing sections disposed around the crank pin in the crank pin hole in the connecting rod. Typically, the prior art semicircular bearing sections are identical to each other and each is provided on its inside surface with at least one circumferentially extending oil feed groove which confronts the crank pin surface. Lubricating oil is fed (at relatively low pressure on the order of 40 psi) through a passage in the crank pin to the oil feed grooves. During operation of the compressor, the crank pin, the connecting rod and the piston move in one direction to effect a gas compression stroke and then move in the opposite direction to effect a suction or return stroke. In the course of the compression stroke, one of the semi-circular bearing sections (i.e., that closest to the piston and typically the "upper" section) is subjected to severe compression forces or load (on the order of 1000 psi) as the driven crank pin moves thereagainst while the gas being compressed resists the corresponding motion of the piston and connecting rod. However, on the return stroke the force on the said one ("upper") bearing section is relieved and only nominal compression force is exerted on the other semi-circular bearing section (i.e., that farthest from the piston and typically the "lower" section). Thus, such severe compressive forces on the "upper" bearing section are frequently repeated and inhibit adequate lubrication during the compression stroke. This eventually results in wear on the inner bearing surface and on the crank pin surface confronting the inner bearing surface of the "upper" bearing section. If the inner surface is grooved, there is eventual formation of a ridge on that ("upper") portion of the crank pin surface confronting the oil feed groove where no such wear occurs. Although elimination of the oil feed groove from the "upper" bearing section would prevent formation of the aforesaid ridge on the crank pin surface, there would also be a substantial loss of direct oil flow to the inside surface of the bearing section and to the confronting crank pin surface and other forms of bearing damage would occur. Since operating temperatures and lubricating oil temperatures in a compressor are typically on the order of 120.degree. F. (and substantially lower than those in an IC engine), the flow of lubricating oil is comparatively slow or sluggish. Furthermore, since oil is supplied to the bearing assembly at a pressure of about 40 psi, but the heavy compressive forces acting on an ungrooved bearing section are on the order of 1000 psi, the force tends to prevent entry of oil between the bearing section and the crank pin thereby causing greater fiction, wear and deformation. Deformation of the crank pin surface and poor lubrication combine to further aggravate and accellerate bearing wear and necessitate costly bearing replacement.
Various types of bearing assemblies have been proposed to overcome lubrication, wear and other problems in various forms of equipment. The following U.S. Pat. Nos. illustrate the state of the art: 3,131,785 Blank 2,566,080 Davids 2,956,642 Chaplin 2,544,913 Brantingham 2,901,297 Sternlicht 2,539,072 Gordon 2,631,905 Coppen 2,289,233 Beall 2,616,771 Metzgar 1,948,340 Dolza 1,947,023 Shoemaker 1,300,023 Riegel
However, none of these patents disclose a construction, mode of operation or solution which is the same as or as effective as that of the present invention.